Creating Libraries

Libraries are simply an indexed collection of object files that are
included as needed in a linked program. Combining object files into a
library makes it easy to distribute your code without disclosing the source.
It also reduces the number of command-line entries needed to compile your
project.

Static Libraries

Executables generated using static libraries are no different than executables
generated from individual source or object files. Static libraries are
not required at runtime, so you do not need to include them when you distribute
your executable. At compile time, linking to a static library is generally
faster than linking to individual source files.

To build a static library:

Use the -c option to generate object files from
the source files:ifort -c my_source1.f90 my_source2.f90
my_source3.f90

Use the GNU ar tool to create the library file
from the object files:ar rc my_lib.a my_source1.o
my_source2.o my_source3.o

If your library file and source files are in different directories,
use the -Ldir option
to indicate where your library is located:

ifort -L/for/libs main.f90
my_lib.a

Shared Libraries

Shared libraries, also referred to as dynamic libraries or Dynamic Shared
Objects (DSO), are linked differently than static libraries. At compile
time, the linker insures that all the necessary symbols are either linked
into the executable, or can be linked at runtime from the shared library.
Executables compiled from shared libraries are smaller, but the shared
libraries must be included with the executable to function correctly.
When multiple programs use the same shared library, only one copy of the
library is required in memory.

To build a shared library:

Use the -fPIC and -c options to generate object files from the source
files:ifort -fPIC -c my_source1.f90
my_source2.f90 my_source3.f90

Use the -shared option
to create the library file from the object files:ifort -shared my_lib.so my_source1.o
my_source2.o my_source3.o